Development information
Dynamic API overview
Creating the tables
Contents
This document contains an overview of the classes involved with creating the tables in the dynamic part of the database.See also
The VirtualDb item is the core item in the process of managing the
dynamic tables. It has a one-to-one relationship with an Experiment.
Thus, each experiment has a separate set of database tables used to store
data for that experiment only. No dynamic tables are created until they are needed. This means
that the creation of a dynamic table is initiated by one of the batcher classes when
it needs to insert data into a particular table. The batcher object calls the
VirtualDb.createTables() method, passing an array of VirtualTable
objects to indicate which tables it needs to create.
The call the proceeds to HibernateUtil.createVirtualTables(). This method uses
the information in the VirtualTable object to find out which columns should be in the
table, and then builds a structure with Hibernate mapping objects. When the structure is
built we use Hibernate to generate the table creation SQL for us.
The SQL is sent to the database using a separate connection. The reason is that some databases (ie. MySQL)
automatically commits a transaction when certain SQL statements are executed (for example CREATE TABLE).
This means that we must be careful to synchronize the two transactions as much as possible. For example,
it is not allowed to create dynamic tables for a VirtualDb item that has not yet been
committed to the database.
The dynamic tables are deleted by the VirtualDb.onAfterCommit() method
if the action parameter is Action.DELETE